I'd like to recommend plants+ on the Berwick Hill road between Seaton Burn and Ponteland, about eight miles north of Newcastle upon Tyne. This is a a real plantman's place, in the middle of nowhere, unburdened by the coffee shops, irrelevant books and godwottery use to pack out so many garden centres. It sells very reasonably priced plants, other horticulural items and pots. The summer hanging baskets are a steal, starting at around £3.99. Many items on 2-4-1 deals. Sign up for their loyalty card which gives you 10% off, even on sale items. Go for a cuppa/snack/lunch at the Northumberland Cheese Farm (signposted) or the cafe at the Milkhope Centre (ditto).